Wood waste biochar promoted anaerobic digestion of food waste: focusing on the characteristics of biochar and microbial community analysis

Abstract

Anaerobic digestion (AD) has been considered as a promising technique for food waste (FW) recycling. However, the accumulation of volatile fatty acids (VFAs) restricts the stability of anaerobic reactors. The present study investigated the use of biochar produced at different conditions (750 °C-30 min, 750 °C-60 min, 750 °C-120 min, 550 °C-60 min, 650 °C-60 min, 850 °C-60 min, 950 °C-60 min) for enhancing the AD of FW. Batch experiments showed that all the biochar increased the methane production rates and biochar obtained at 750 °C-60 min resulted in the highest enhancement by 21.5%. It was further showed surface oxygen-containing functional groups and graphitization degree of biochar were the critical factors for improving methane production. Microbial analysis showed that biochar addition formed different microbial communities, and Methanosaeta, Romboutsia, and norank_f_Anaerolineaceae were enriched, which might be correlated with direct interspecies electron transfer (DIET). This research showed biochar could enhance the AD of FW and also revealed the main characteristics of biochar relating with the enhancement of AD. Graphical Abstract

Hydrochar-Promoted Methane Production in Mesophilic and Thermophilic Anaerobic Digestion of Hydrothermal Pre-Treated Sludge

“…Hydrochar significantly influenced the biodiversity during the AD of hydrothermal pre-treated sludge (Figure 6a). The Shannon index serves as a measure of biodiversity or species diversity within a given ecological community, with higher values indicating greater diversity and lower values suggesting lower diversity in the community [29]. The Shannon index in the four groups of reactors follows this order: MH > HH > MC > HC.…”

“…Reactors with hydrochar addition reached their lowest pH earlier than those without hydrochar, and the pH remained more stable during AD compared to the reactors without hydrochar. This observation could be associated with dominant functional microorganisms in the system and variations in microbial substrate metabolic pathways [21,29]. From the 12th to the 16th day of the experiment, the VFAs in the reactors were rapidly consumed and converted into CH4 and CO2, leading to a gradual increase in pH.…”

“…The total genomic DNA was collected using the PowerMax Soil DNA Isolation Kit (MoBio Laboratories, Carlsbad, CA, USA) [29]. The quality of the genomic DNA was assessed using Nanodrop ND-2000c (Thermo Fisher Scientific, Waltham, MA, USA).…”

“…Hydrochar addition also resulted in a notable rise in the relative abundance of Synergistota and Firmicutes in the MH and HH groups compared to the MC and HC groups without hydrochar addition. Some microorganisms belonging to Synergistota possess the capability to degrade peptides, amino acids, and proteins, the augmented relative abundance of which plays a role in converting complex organic matter in hydrothermal pre-treated sludge into small-molecule substances, thereby promoting methane production in subsequent processes [29]. Firmicutes have also been documented to be the prevailing microorganisms in AD reactors [43].…”

A Wooden Carbon-Based Photocatalyst for Water Treatment

“…Biochar is a kind of carbon-rich material that is produced by pyrolysis (anaerobic heating) of biomass [22], such as wood [23], agricultural residues [24] and other organic materials [25]. In recent years, it has attracted great attention because of its potential applications in various fields, including environmental restoration, water treatment, agriculture and energy production [26,27].…”